Plasma processing apparatus and method of plasma processing

ABSTRACT

Plasma processing apparatus and plasma processing methods capable of maintaining acceptable etching characteristics and to prevent degradation of a lower electrode even when the focus ring is severely eroded by the plasma, while leaving the plasma discharge conditions used in the conventional apparatus and methods substantially unchanged, are disclosed. According to an exemplary embodiment, a side-surface protecting ring formed of a ceramic material is provided to cover the side surface of the lower electrode such that an outer perimeter of the side-surface protecting ring is approximately aligned with, or inside, an outer perimeter of the substrate to be processed. As a result, the side-surface protecting ring does not influence the plasma characteristic.

This invention is first described in a Japanese Application No. 2004-53275, which is incorporated by reference in its entirety.

BACKGROUND

This invention relates to a plasma processing apparatus for processing a surface of a substrate using plasma and also relates to methods of plasma processing a surface of a substrate.

Plasma processing techniques, such as, for example, dry etching techniques, have been widely used for manufacturing semiconductor devices such as semiconductor integrated circuits. The plasma processing processes various films formed on a surface of a substrate to be processed, such as a semiconductor wafer, using reactive gases activated by plasma. The dry etching, for example, etches various films and forms fine circuit patterns such as electrode and wiring patterns using resist patterns formed by the lithography as masks.

In any application of the plasma processing, it is inevitable that the reactive gas activated by the plasma touches and erodes components within the processing chamber. Especially, the processing of silicon oxide films requires high radio frequency power, because the bonding energy of Si—O bonds is high. Accordingly, the processing of silicon oxide films causes severe damage to the components.

In general, so-called parallel-plate RIE (Reactive Ion Etching) apparatus is mainly used as the dry etching apparatus for processing silicon oxide films. In the parallel-plate RIE apparatus, radio-frequency power is applied to upper and lower electrodes that face in parallel with each other. In such an apparatus, usually, the wafer to be processed is placed on the lower electrode and the plasma is concentrated between the electrodes to process the surface of the wafer.

In order to concentrate the plasma between the electrodes, peripheries of the upper and the lower electrodes are surrounded by ring-shaped components formed of, for example, quartz. Hereafter, the ring-shaped component that surrounds the upper electrode will be called “shield ring”, while the ring-shaped component that surround the lower electrode will be called “focus ring”.

Moreover, in order to improve processing accuracy, an electrostatic chuck has been widely employed as the means to hold the wafer on the wafer-supporting surface of the plasma processing apparatus. Compared with a mechanical chuck, the electrostatic chuck improves the uniformity of the surface temperature of the wafer and improves the uniformity of the processing.

Electrostatic chucks are generally classified into two types. One is formed of fluorocarbon resin, and the other is formed of ceramics. The dry etching apparatus for processing silicon oxide films mainly utilize the electrostatic chuck formed of fluorocarbon resin, in which a conductive film is inserted into a fluorocarbon resin film. A high DC voltage is applied to the conductive film, and the wafer is chucked onto the upper surface of the electrostatic chuck by the Coulomb force generated between the wafer and the conductive film.

FIG. 10 is a partial cross-sectional view showing the periphery of the lower electrode of a plasma processing apparatus. As shown in FIG. 10, the upper surface 118 a of the lower electrode 118 has an electrostatic chuck 120, which is formed of, for example, a fluorocarbon resin film 120 a and a conductive film 120 b inserted within the resin film 120 a. The fluorocarbon resin film 120 a also covers the side surface 118 b of the lower electrode 118.

A focus ring 124 is detachably placed so as to surround the periphery of the lower electrode 118. The wafer to be processed is placed on the upper surface of the electrostatic chuck 120 and is chucked by the electrostatic chuck. That is, the wafer W to be processed is supported on the upper surface, or the wafer-supporting surface, 118 a of the lower electrode via the electrostatic chuck 120.

In the dry etching apparatus for processing silicon oxide films described above, a component that is generally most severely damaged by the plasma is the focus ring 124 that surrounds the lower electrode 118. When the focus ring is continuously used in the processing apparatus, it gradually erodes. The erosion generally proceeds in the vertical direction, mainly at the stepped region 124 a near the inner perimeter of the focus ring 124, and a groove is formed. In other words, the erosion proceeds mainly at the area near the outer perimeter of the wafer W.

When the erosion reaches the extent shown in FIG. 11, the side surface of the lower electrode 118 b becomes exposed to the plasma. Although the side surface 118 b is covered with the fluorocarbon resin film 120 a, the fluorocarbon resin film 120 a is thin. Therefore, the plasma may influence the temperature of the wafer W chucked by the electrostatic chuck 120 onto the supporting surface 118 a of the lower electrode 118.

As discussed above, the control of the wafer temperature is crucial for etching fine patterns. However, as discussed above, the amount of plasma radiation to the lower electrode 118 increases as the erosion of the focus ring 124 increases. The increased plasma radiation increases the surface temperature of the wafer W, especially at the region near the edge. As a result, it becomes difficult to maintain an acceptable uniformity of etching.

Moreover, exposure of the lower electrode 118 to the plasma accelerates the degradation and shortens the usable life of the lower electrode 118. The lower electrode 118, to which the electrostatic chuck 120 is attached, is one of the most expensive components in the dry etching apparatus. Therefore, the shortened life of the lower electrode 118 markedly increases the operation cost of the apparatus.

As such, the erosion of the focus ring 124 causes two problems, change of the etching characteristics, and rapid degradation of the lower electrode 118. Therefore, the focus ring 124 is generally replaced or repaired at short intervals before it becomes severely damaged. As a result, the replacement and/or repair of the focus ring has to be made frequently, and the throughput and the cost of production of semiconductor devices by the processing apparatus are thus adversely affected.

In regards to the focus ring that is eroded by the plasma, various improvements have been proposed in, for example, the following references:

Japanese Laid-open Patent No. 2003-100713 (Patent Document 1) discloses an electrode cover which is divided into an inner portion and an outer portion. The inner portion, which is further divided into a plurality of sections in the circumferential direction, surrounds the side surface of the lower electrode. The outer portion is attached to the outside of the inner portion. Thereby, a plurality of sections and portions are combined to form a cover, or a focus ring, having an inner periphery that surrounds closely the side surface of the lower electrode.

Japanese Laid-open Patent No. 8-339895 (Patent Document 2) discloses a quartz component, or a focus ring, coated with an insulating film having a high resistance to the erosion by the plasma. Specifically, the Patent Document 2 proposes to form a layer of an insulating film having a high resistance to the erosion, such as a layer of alumina ceramics, on a surface of the quartz component that faces the plasma.

Japanese Laid-open Patent No. 2-130823 (Patent Document 3), hereby incorporated by reference in its entirety, discloses a ring for covering the periphery of a lower electrode, which is composed of an inner alumina ring and an outer fluorinated resin ring. Specifically, the alumina ring disclosed in the Patent Document 3 covers the side surface of the lower electrode and further extends outwardly so that a portion of the alumina ring is exposed to the plasma at a position adjacent to the outer perimeter of the substrate to be processed. Patent Document 3 describes that the plasma, which erodes the fluorinated resin ring, does not erode the alumina ring, and that the alumina ring enables to maintain the etching uniformity for a long period of time.

The focus ring disclosed in Patent Document 1 aims to minimize the clearance between the lower electrode and the focus ring, but does not suppress the erosion of the focus ring.

In the quartz component disclosed in Patent Document 2, the insulating film having a high erosion resistance is coated on the surface of a quartz component, which is designed to have a shape suitable to be used in a processing apparatus. Therefore, the thickness of the resistive coating film is limited so that the coating film does not materially change the shape of the component. Therefore, the ability to improve the erosion resistance is limited.

Further, in Patent Document 2, charged particles in the plasma accelerated toward a direction perpendicular to the surface of a substrate to be processed irradiate the insulating film. Similarly, in Patent Document 3, charged particles in the plasma accelerated toward the direction perpendicular to the surface of a substrate irradiate the portion of the alumina ring. Therefore, the insulating film, which has a secondary electron emission coefficient different from that of the quartz component, or the alumina ring, which has a secondary electron emission coefficient different from that of the fluorinated resin ring, influences the plasma characteristics.

As a result, plasma discharge conditions used in a conventional plasma processing apparatus that does not have the insulating film of Patent Document 2 or the alumina ring of Patent Document 3 may not be used when the insulating film or the alumina ring is adapted in the processing apparatus. Accordingly, neither of the insulating film proposed in Patent Document 2 nor the alumina ring proposed in Patent Document 3 is suitable as a means to, for example, retrofit an existing apparatus.

SUMMARY

Accordingly, in order to solve the above-mentioned problems, an exemplary object of this invention is to provide an apparatus and methods to maintain acceptable etching characteristics even when the focus ring is severely eroded, while leaving the plasma discharge conditions used in the conventional apparatus and methods substantially unchanged. Another exemplary object of this invention is to provide an apparatus and methods that diminish the degradation of the lower electrode even when the focus ring is severely eroded, while leaving the plasma discharge conditions used in the conventional apparatus and methods substantially unchanged.

In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing apparatus for processing a substrate using plasma. The exemplary apparatus includes a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, a side surface protecting ring that covers the side surface of the lower electrode, and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring. The supporting surface may have a dimension approximately the same as, or smaller than, a dimension of the substrate. The side surface protecting ring may be formed of a ceramic material, and an outer perimeter of the side surface protecting ring may be approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface. The focus ring is formed of a first material different from the first material.

In the exemplary apparatus, an outer perimeter of the side surface protecting ring may be positioned inside of an outer perimeter of the substrate supported on the supporting surface.

Furthermore, in the exemplary apparatus, the ceramic material may be selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution, and the first material may be selected from a group consisting of quartz, silicon, and engineering plastics.

In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing apparatus for processing a substrate using plasma. The exemplary apparatus includes a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, a side surface protecting ring that covers the side surface of the lower electrode, and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring. The supporting surface may have a dimension smaller than a dimension of the substrate. The side surface protecting ring may be formed of a ceramic material, and an outer perimeter of the side surface protecting ring may be approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface. The focus ring may be formed of quartz.

In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing method of processing a substrate using plasma. The exemplary method includes providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material, and surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material different from the ceramic material. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate. The exemplary method further includes supporting the substrate on the supporting surface, and processing a surface of the substrate by generating plasma in the processing chamber. Processing the surface includes i) preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode, and ii) preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.

In the exemplary method, the focus ring may prevent the plasma from touching the side surface protecting ring before the focus ring is eroded by the plasma, and the side surface protecting ring may prevent the plasma from touching the side surface of the lower electrode even after the focus ring is eroded by the plasma to an extent that the focus ring cannot prevent the plasma from touching the side surface of the lower electrode.

Furthermore, in the exemplary method, the covering may include positioning an outer perimeter of the side surface protecting ring approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface.

In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing method of processing a substrate using plasma. The exemplary method includes providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material, and surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of quartz. The supporting surface may have a dimension smaller than a dimension of the substrate. The exemplary method further includes supporting the substrate on the supporting surface, and processing a surface of the substrate by generating plasma in the processing chamber. Processing the surface includes i) preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode, and ii) preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an exemplary plasma processing apparatus according to an exemplary embodiment of this invention;

FIG. 2 is a magnified view showing the relationship between the focus ring and the lower electrode, to which the ceramic ring is fitted, in the plasma processing apparatus shown in FIG. 1;

FIG. 3 is a graph illustrating a relationship between the amount of erosion of the focus ring and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;

FIG. 4 is a graph illustrating a relationship between the temperature near the edge of a wafer and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;

FIG. 5 is a cross-sectional view showing the structure of a wafer W processed in an exemplary plasma processing apparatus;

FIG. 6 is a graph illustrating a relationship between the etching rate of silicon dioxide film near the edge of the wafer and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;

FIG. 7 is a graph illustrating a relationship between the etching rate of silicon dioxide film near the edge of the wafer and the cumulative RF discharge time of the focus ring in an exemplary plasma processing apparatus according to this invention;

FIG. 8 is a graph illustrating a relationship between the silicon dioxide etching rate near the edge of the wafer and the cumulative RF discharge time of two focus rings used alternately in the exemplary plasma processing apparatus according to this invention;

FIG. 9 is a graph illustrating a relationship between the amount of erosion of the ceramic ring and the cumulative RF discharge time of the ceramic ring;

FIG. 10 is a magnified view showing the relationship between an uneroded focus ring and the lower electrode in a conventional plasma processing apparatus; and

FIG. 11 is a magnified view showing the relationship between an eroded focus ring and the lower electrode in a conventional plasma processing apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

An exemplary plasma processing apparatus and plasma processing methods according to this invention are explained in detail with reference to various exemplary embodiments shown in the drawings.

FIG. 1 is a schematic drawing of an exemplary plasma processing apparatus according to this invention. As shown in FIG. 1, an exemplary plasma processing apparatus 10 is a dry etching apparatus for manufacturing semiconductor devices. The apparatus 10 may have a narrow-gap parallel-plate construction and etches oxide films such as silicon oxide films using high-frequency (radio frequency) plasma.

The processing chamber 12 for accommodating a wafer W, which is a substrate to be processed, can be evacuated to a pressure of, for example, about 10⁻⁶ Torr (10⁻⁴ Pa). Various components are provided within the chamber 12.

In the upper center of the chamber 12, an upper electrode 16, which is connected to a gas inlet 14 for introducing an etching gas, is provided. In the lower center of the chamber 12, a lower electrode 18 is provided.

According to various exemplary embodiments, the lower electrode 18 is formed of alumite-coated aluminum. The upper surface (a wafer-supporting surface) 18 a of the lower electrode 18, has a dimension approximately the same as or is slightly smaller than the dimension of the wafer W. The inside of the lower electrode 18 has a circulation path for circulating coolant supplied from the chiller (not shown), which is placed outside the chamber 12. Thereby, the upper surface 18 a of the lower electrode 18 can be maintained to a desired temperature.

According to various exemplary embodiments, on the upper surface 18 a of the lower electrode 18, an electrostatic chuck 20 for chucking the wafer W is provided. The electrostatic chuck 20 is formed of a fluorocarbon resin film 20 a in which a metal film 20 b is inserted. The fluorocarbon resin film, forming the electrostatic chuck 20, also covers the side surface 18 b of the lower electrode 18.

Applying a voltage to the metal film from a high voltage DC power source (not shown), which is placed outside of the chamber 12, produces a Coulomb force between the metal film 20 b and the wafer W. Thereby, the wafer W is chucked on the upper surface of the electrostatic chuck 20. Thereby, the wafer W is supported on the wafer-supporting surface 18 a of the lower electrode 18 by the electrostatic chuck 20. The height of the upper surface 24 b of the focus ring 24 generally matches the height of the upper surface of the wafer W supported on the wafer supporting surface 18 a.

According to various exemplary embodiments, the lower electrode 18 also has passages (not shown) to supply He gas. Supplying He gas to the back side of the wafer W chucked on the electrostatic chuck 20 improves the thermal conduction between the wafer W and the lower electrode 18. The passages are divided into two groups so that the pressures of He gas supplied to the central portion and to the outer portion of the wafer W can be controlled independently.

According to various exemplary embodiments, on the side surface 18 b of the lower electrode 18, a side-surface protecting ring 30 formed of a ceramic material (which will be called as a “ceramic ring” hereinafter) is placed. That is, the ceramic ring 30 covers the side surface 18 b of the lower electrode 18, or, more exactly, the fluorocarbon resin film 20 a covering the side surface 18 b of the lower electrode 18.

A shield ring 22 and a focus ring 24 surround peripheries of the upper electrode 16 and of the lower electrode 18, respectively. The shield ring 22 and the focus ring 24 concentrate the plasma between the parallel-plate electrodes. The shield ring 22 and the focus ring 24 are detachable in order to perform, for example, a mechanical cleaning.

According to various exemplary embodiments, a RF power splitter 26 and a RF power generator 28 are placed outside of the chamber 12. The RF power generator 28 supplies a high-frequency (radio frequency) power to the RF power splitter 26, and the RF power splitter 26 applies RF power to both the lower electrode 18 and the upper electrode 16. Thus, RF plasma is generated within the chamber 12 and dry etching is performed.

The plasma processing apparatus 10 shown in FIG. 1 employs, as an example, a split-coupling configuration by using the RF power splitter 26. However, any one of the configurations including an anode-coupling, a cathode-coupling, or a split-coupling configurations may be selected.

FIG. 2 is a magnified view showing the relationship between the lower electrode 18, to which the ceramic ring 30 is fitted, and the focus ring 24.

According to various exemplary embodiments, the ceramic ring 30 has a ring shape, and is formed of a ceramic material having an erosion rate by the plasma lower than that of the material forming the focus ring 24.

According to various exemplary embodiments, the side surface 18 b of the lower electrode 18 is covered with the fluorocarbon resin film 20 a that constitutes the electrostatic chuck 20, and is surrounded by the focus ring 24. The ceramic ring 30 is inserted between the fluorocarbon resin film 20 a covering the side surface 18 b of the lower electrode 18 and the inner-side surface of the focus ring 24. That is, the side surface 18 b of the lower electrode 18 is covered by the fluorocarbon resin film 20 a and further by the ceramic ring 30, and then surrounded by the focus ring 24.

In the exemplary plasma processing apparatus 10 shown in FIG. 2, the ceramic ring 30 has a thickness (a dimension perpendicular to the side surface 18 b of the lower electrode) such that it is fitted inside the outer perimeter of the wafer W.

When the erosion of the focus ring 24 reaches a certain extent, the ceramic ring 30 becomes directly exposed to the plasma. Therefore, the ceramic ring 30 should preferably have a sufficient thickness in order to improve the durability and the mechanical strength.

However, if the ceramic ring 30 is too thick and extends outwardly from the outer perimeter of the wafer W, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the wafer W may irradiate the surface of the ceramic ring 30. As a result, the plasma characteristics may change due to the difference between the secondary electron emission coefficients of the ceramic ring 30 and the quartz focus ring 24. Such change in the plasma characteristics changes the etching characteristics. Thus, the etching condition should be adjusted differently. Further, depending on the etching process, small particles emitted from the ceramic ring may alter the electrical characteristics of the semiconductor device processed by the apparatus.

Thus, it is preferable to make the dimension of the wafer-supporting surface 18 a of the lower electrode 18 smaller than that of the wafer W, and position the outer perimeter, or the outer surface, of the ceramic ring 30 approximately aligned with, or inside, the outer perimeter of the wafer W.

According to the various exemplary embodiments of this invention, the fluorocarbon resin film 20 a on the side surface 18 b of the lower electrode 18 may be omitted. The material of the focus ring 24 is not limited to quartz. For example, silicon may be used as the material to form the focus ring 24. Kinds of engineering plastics having high operation temperatures, which are also called super engineering plastics, may also be used. For example, Vespel® Polyimide from DuPont, and Celazole® PolyBenzlmidazole from Celanese Advanced Materials may be used.

The material of the side-surface protecting ring 30 may preferably be, for example, alumina, but is not limited to specific materials among various ceramic materials. Other ceramic materials such as aluminum nitride, silicon nitride, and silicon carbide may also be used. Further, at least in processing apparatus for use in BEOL (Back-end of the line) processes in the semiconductor device production, zirconia, titanium nitride, and YGA (Y₃Al₅O₁₂) may also be used. Moreover, solid solutions including one or more of these materials, such as alumina-silicate solid solution, alumina-silicon nitride solid solution, and the like, may also be used. These ceramic materials may contain various additives.

Different materials among the above-mentioned materials for the focus ring 24 have different erosion rates by the plasma. Also, different materials among the ceramic materials described above have different erosion rates by the plasma. The erosion rates also vary depending on various conditions such as the processing gas and the plasma discharge condition. Further, the actual erosion rates of the materials forming the focus ring 24 and the ceramic ring 30 also vary depending on the positions of the components fitted in the plasma processing apparatus 10. In general, however, the ceramic materials described above have lower erosion rates that those of the materials used for forming the focus ring 24.

According to various exemplary embodiments, in order to perform etching using the plasma processing apparatus 10, after evacuating the chamber 12 to a predetermined pressure, a fluorocarbon-based etching gas is introduced from the gas inlet 14, and an etching gas atmosphere with a predetermined pressure is produced within the space between the electrodes 16 and 18. By applying an RF power, through the RF power splitter 26, to the electrodes 16 and 18 between which the etching gas atmosphere is produced, fluorocarbon-based plasma is generated. As a result, charged particles within the plasma are accelerated toward the direction perpendicular to the surface of the wafer W placed on the wafer-supporting surface 18 a of the lower electrode 18, and the surface of the wafer W becomes etched.

In the various exemplary embodiments according to this invention, the side surface of the lower electrode 18 is protected by a ceramic ring 30 formed of a material having a lower erosion rate than that of the material of the focus ring 24. Therefore, even after the focus ring 24 is severely eroded, the side surface 18 b of the lower electrode 18 is not exposed to the plasma and is not damaged. As a result, increase of the surface temperature near the edge of the wafer W is diminished, and the acceptable etching characteristics can be maintained.

Moreover, because the etching characteristics can be maintained even after the focus ring is severely eroded, the interval for replacing the focus ring 24 can be extended. As a result, the costs incurred for the maintenance is reduced.

Furthermore, because the ceramic ring 30 protects the side surface 18 b of the lower electrode 18, the mechanical damage to the fluorocarbon resin film covering the side surface 18 b of the lower electrode 18 during the attaching and detaching of the focus ring 34 is prevented.

In the exemplary plasma processing apparatus, before the erosion of the focus ring proceeds, the wafer W and the focus ring 24 prevent the ceramic ring 30 and the side surface 18 b of the lower electrode 18 from being exposed to the plasma. After the focus ring 24 is eroded to an extent that it cannot prevent the ceramic ring 30 from being exposed to the plasma, the ceramic ring 30 then prevents the side surface 18 b of the lower electrode 18 from being exposed to the plasma. In other words, after the focus ring 24 is eroded to an extent that the focus ring 24 alone cannot prevent the side surface 18 b of the lower electrode 18 from being exposed to the plasma, the ceramic ring 30 prevents the side surface 18 b of the lower electrode 18 being exposed to the plasma.

Moreover, in the exemplary embodiment of the plasma processing apparatus 10, the dimension of the wafer-supporting surface 18 a of the lower electrode 18 is made smaller than the dimension of the wafer W, and the outer perimeter of the ceramic ring 30 is positioned approximately aligned with, or inside, the outer perimeter of the wafer W. Accordingly, it is possible to prevent charged particles in the plasma accelerated to the direction perpendicular to the surface of the wafer W from irradiating the ceramic ring 30, even after the focus ring 24 is eroded.

When the outer perimeter of the ceramic ring 30 is positioned inside of the outer perimeter of the wafer, the entire portion of the ceramic ring 30 is prevented from being irradiated by the charged particles in the plasma accelerated toward the direction perpendicular to the surface of the wafer W.

When the dimension of the ceramic ring 30 is designed such that it can be fitted to the lower electrode 18 with its outer perimeter aligned with the outer perimeter of the wafer W supported on the wafer-supporting surface 18 a, minor portions of the periphery of the ceramic ring 30 may extend outwardly from the outer perimeter of the wafer W due to inadvertent variations in the dimensions and the positions of the ceramic ring 30 and the wafer W. That is, in practice, the outer perimeter of the ceramic ring 30 aligns only approximately with the outer perimeter of the wafer W.

The extended portions of the ceramic ring 30 may be irradiated by the accelerated charged particles. Nonetheless, irradiation of the remaining portions of the ceramic ring 30 by the accelerated charged particles is prevented. Therefore, the area of the portions of the ceramic ring 30 irradiated by the accelerated charged particles is far smaller than the case that the dimension of the ceramic ring 30 is designed to extend outwardly from the outer perimeter of the wafer W.

As a result, even if the secondary electron emission coefficient of the ceramic material used for forming the ceramic ring 30 is different from that of the material for forming the focus ring 24, the ceramic ring 30 does not materially influence the plasma characteristics. Therefore, a plasma discharge condition used in a conventional plasma processing apparatus that does not have a ceramic ring may be used essentially unchanged in the processing apparatus 10 having the ceramic ring 30.

The exemplary plasma processing apparatus and plasma processing methods according to this invention are not limited to the embodiments described above. For example, the plasma processing apparatus may be any type of plasma processing apparatus that comprises an electrode having a substrate-supporting surface. Further, the exemplary plasma processing apparatus according to this invention is not limited to semiconductor manufacturing apparatuses for processing surfaces of semiconductor substrates, but may be various apparatuses for processing various other substrates. Moreover, various reaction gases other than the fluorocarbon-based gas may be used.

COMPARATIVE EXAMPLE 1

In order to confirm the effect of the ceramic ring 30 in the exemplary plasma processing apparatus 10, etching is performed using a conventional plasma processing apparatus that does not have a ceramic ring 30.

FIG. 3 is a graph illustrating a relationship between an amount of erosion of the focus ring 124 of a conventional plasma processing apparatus in the vertical direction, or in the direction perpendicular to the surface of the wafer W supported on the wafer-supporting surface 118 a, and a cumulative RF discharge time of the focus ring 124 (i.e., a cumulative time of RF discharge made using the same focus ring 124).

FIG. 11 described above shows the shape of the focus ring 124 when the amount of erosion is about 1 mm. FIG. 3 indicates that the focus ring 124 reaches this shape when the cumulative RF discharge time reaches about 300 hours. It is found that the desired etching characteristics cannot be maintained when the focus ring 124 has the shape shown in FIG. 11.

At first, in order to investigate the relationship between the surface temperature of the wafer W and the amount of erosion of the focus ring 124, the surface temperature of the wafer W is measured while the plasma is generated. Specifically, the surface temperature of the wafer W at 5 mm from the edge is measured.

As the dry etching process gas, a mixture of etchant gases (CF₄ and C₄F₈), CO and Ar is used. Table 1 shows the plasma discharge condition during the measurement of the surface temperature. However, the plasma processing apparatus is used for the production of semiconductor devices with a different process gas and a different plasma discharge condition shown in Table 2. That is, the focus ring 124 is mainly eroded by the plasma with the condition shown in Table 2. TABLE 1 RF Coolant temperature Back side Discharge Power Gas flow [° C.] He pressure pressure density rate [sccm] upper lower [Torr] [mTorr] [Wcm⁻²] CF₄ C₄F₈ CO Ar electrode electrode center edge 150 4.65 10 8 120 350 30 −10 10 19

TABLE 2 Coolant Back side Discharge RF Gas flow temperature [° C.] He pressure pressure Power density rate [sccm] upper lower [Torr] [mTorr] [Wcm⁻²] CF₄ CHF₃ Ar electrode electrode center edge 300 4.65 40 30 500 30 −10 10 22

FIG. 4 is a graph illustrating the result of measurements, where the surface temperature near the edge of the wafer W is shown in relation to the cumulative RF discharge time of the focus ring 124. FIG. 4 indicates that the surface temperature near the edge of the wafer W increases after the cumulative RF discharge time exceeds 300 hours due to the increased radiation of the plasma to the side surface 118 b of the lower electrode 118.

As shown in FIG. 11, the side surface 118 b of the lower electrode is covered by the fluorocarbon resin film 120 a. Therefore the side surface 118 b of the lower electrode 118 is not directly exposed to the plasma, but is only exposed to the plasma through the fluorocarbon resin film 120 a. Because the fluorocarbon resin film 120 a is thin, however, the heat energy received from the plasma easily reaches the lower electrode 118.

Further, a coolant with the temperature shown in Table 1 is circulated within the lower electrode 118. Because there is a certain distance between the circulation path and the side surface 118 b of the lower electrode 118, however, the temperature of the lower electrode 118 near the side surface 118 b increases when the side surface 118 b is exposed to the plasma. Accordingly, the temperature of the edge portion of the wafer W increases.

In order to evaluate the change of etching rate of small holes near the edge of the wafer W by the increase of the cumulative RF discharge time of the focus ring, dry etching is conducted. Specifically, the surface of the wafer W shown in FIG. 5 is etched under the conditions shown in Table 1.

As discussed above, however, the apparatus is used for the production with the condition shown in Table 2. Here, the condition shown in Table 1 is more suitable for etching small holes, but is more strongly influenced by the surface temperature of the wafer W.

According to various exemplary embodiments, in the wafer W shown in FIG. 5, on a silicon substrate S1, a 2.0 μm thick silicon dioxide film S2 is formed, and a 1.2 μm thick photoresist mask pattern M is formed on the silicon dioxide film. The mask M has 0.30 μm^(Φ) holes H. A mixture of etchant gases (CF₄ and C₄F₈) and CO and Ar is used as the dry etching process gas. The etching rate is measured at the position of 5 mm from the edge of the wafer W.

FIG. 6 is a graph illustrating the change of the silicon dioxide film etching rate in relation to the cumulative RF discharge time of the focus ring 124. FIG. 6 shows that the etching rate near the edge of the wafer W significantly decreases after the cumulative RF discharge time exceeds 300 hours.

This result indicates that, 1) when the cumulative RF discharge time exceeds 300 hours, the focus ring 124 is severely damaged and irradiation of the plasma to the side surface of the lower electrode 118 increases, and 2) as a result, the surface temperature near the edge of the wafer W increases and the etching rate near the edge of the wafer W decreases. In other words, it is impossible to maintain acceptable etching characteristics when the cumulative RF discharge time exceeds 300 hours.

Moreover, in the conventional plasma processing apparatus illustrated in FIG. 10, the lower electrode 118 is also damaged when the erosion of the focus ring 124 proceeds to the extent shown in FIG. 11.

The fluorocarbon resin film 120 a covering the side surface 118 b of the lower electrode 118 is not highly resistant to the plasma. Therefore, when the focus ring 124 is eroded as shown in FIG. 11, the fluorocarbon resin film 120 a on the side surface 118 b of the lower electrode 118 may easily be degraded. Moreover, in the conventional plasma processing apparatus illustrated in FIGS. 10 and 11, it is difficult to prevent the fluorocarbon resin film 120 a on the side surface 118 b from being damaged during attaching and detaching of the focus ring 124.

As a result, when the focus ring 124 is severely eroded as shown in FIG. 11, the fluorocarbon resin film 120 a disappears at least partly on the side surface 118 b of the lower electrode 118, and portions of the side surface 118 b of the lower electrode 118 are directly exposed to the plasma. The direct exposure to the plasma degrades the alumite coating on the side surface 118 b of the lower electrode 118, and causes abnormal discharge, or arcing, from the portion that is dielectrically destructed.

When the abnormal discharge occurs, the lower electrode 118 cannot be used anymore. Therefore, the operation of the apparatus must be stopped, and the replacement to a new lower electrode 118 must be made.

As discussed above, in the conventional plasma processing apparatus that does not have the ceramic ring 30, the etching rate changes and the lower electrode degrades when the focus ring 124 is eroded. Therefore, the focus ring 124 should be replaced when the cumulative RF discharge time exceeds 300 hours, or when the amount of erosion in the vertical direction reaches about 1 mm by a visual inspection. The used focus ring 124 should be discarded or repaired.

EXAMPLE 1

Using the exemplary plasma processing apparatus 10 shown in FIG. 1, dry etching of silicon dioxide films S2 on the surface of the wafers W shown in FIG. 5 is conducted, and the change of the etching rate is examined.

As shown in FIG. 2, the ceramic ring 30 has a dimension such that the outer perimeter of the ceramic ring 30 is positioned inside of the outer perimeter of the wafer W. Specifically, the dimension, or the diameter, of the wafer-supporting surface 18 a of the lower electrode 18 is about 6 mm smaller than that of the wafer W, and the thickness, or the width, of the ceramic ring 30 is 2 mm. Therefore, the outer perimeter of the ceramic ring 30 is positioned about 1 mm inside the outer perimeter of the wafer W. In this example, the material of the ceramic ring is alumina.

In this example, a focus ring 24 that is already severely eroded is used. Specifically, a focus ring 24 that is already eroded to a depth of 3 mm in the vertical direction at the stepped portion 24a near the inner perimeter, which faces the lower electrode 18, is used. This amount of erosion corresponds to three times the maximum allowable erosion depth (1 mm) in a conventional apparatus. In other words, a focus ring that has been used for a cumulative RF discharge time of about 900 hours, is used.

The etching for measuring the etching rate is conducted using the plasma discharge condition shown in Table 3. The apparatus 10 is also used for the production of semiconductor devices using the condition shown in Table 2. TABLE 3 RF Coolant temperature Back side Discharge Power Gas flow [° C.] He pressure pressure density rate [sccm] upper lower [Torr] [mTorr] [Wcm⁻²] CF₄ C₄F₈ CO Ar electrode electrode center edge 150 4.65 10 8 120 350 30 −10 10 16

According to various exemplary embodiments, when the ceramic ring 30 is fitted around the side surface 18 b of the lower electrode 18, the surface temperature within about 5 mm from the edge of the wafer decreases with an amount of about 5° C. if the discharge condition shown in Table 1 is used. Such decrease in the temperature is due to the fact that, different from the conventional apparatus, the side surface 18 b of the lower electrode 18 is not exposed to the plasma, and the thermal conductivity of the ceramic ring 30 is high. Especially, the fact that the ceramic ring 30 is made of alumina having a thermal conductivity more than 20 times higher than that of quartz, which is the material of the focus ring 30, significantly improves the cooling efficiency of the edge portion of the wafer W.

Therefore, according to various exemplary embodiments, in order to improve the uniformity of the surface temperature of the wafer W, the condition shown in Table 3 is used to measure the etching rate. Specifically, as shown in Table 3, the pressure of He gas supplied to the peripheral portion of the back side of the wafer W is decreased to an amount of about 3 Torr, compared to the condition shown in Table 1. Otherwise the condition shown in Table 3 is the same as that shown in Table 1.

FIG. 7 is a graph illustrating the change of the silicon dioxide film etching rate in relation to the cumulative RF discharge time of the focus ring 24. As shown in FIG. 7, the etching rate of 0.30 μm^(Φ) hole does not significantly change even when the focus ring 24, which has already been eroded to the depth of 3 mm, is further used for 400 hours.

This result indicates that the ceramic ring 30 enables to maintain a uniform surface temperature of the wafer W and a stable etching rate irrespective of the amount of erosion of the focus ring 24. Further, because the etching rate is stable irrespective of the amount of erosion, the usable life of the focus ring 24 can be extended.

That is, according to various exemplary embodiments of this invention, a protecting ring formed of a ceramic material that has an erosion rate lower than that of the material of the focus ring covers the side surface of the lower electrode. Accordingly, even after the focus ring is severely eroded, acceptable etching characteristics can be maintained and the degradation of the lower electrode is prevented. Moreover, an interval to replace the focus ring can be extended, and a cost incurred for replacing the focus ring can be reduced.

Moreover, as discussed above, it is not necessary to materially change the etching condition when the ceramic ring 30 is used. Specifically, the etching condition shown in Table 3, which is the same as the conventional condition shown in Table 1, except that the pressure of He supplied to the back side of the wafer W is adjusted, can be used in the apparatus 10 that utilizes the ceramic ring 30. This result indicates that the ceramic ring 30 does not materially influence the plasma characteristics.

In this exemplary embodiment, because a focus ring 24 that is already severely eroded is used, the ceramic ring 30 is exposed to the plasma. Because the outer perimeter of the ceramic ring 30 is positioned inside of the outer perimeter of the wafer W, however, charged particles in the plasma accelerated toward the direction perpendicular to the surface of the wafer W do not irradiate the ceramic ring 30. Accordingly, the ceramic ring 30 does not materially change the plasma characteristics.

EXAMPLE 2

Using the plasma processing apparatus 10 shown in FIG. 1, an exemplary etching process is performed for a plurality of wafers W having the structure shown in FIG. 5. The thickness of the ceramic ring 30 is 2 mm. Two focus rings 24, which have not been eroded, are prepared, and a running experiment is conducted by alternately using the two focus rings 24. That is, the operation of the apparatus 10 is stopped every 50 hours of cumulative RF discharge time for a mechanical cleaning. During the mechanical cleaning, the focus ring 24 is substituted with another one.

Measurement of the etching rate of 0.30 μm^(Φ) hole is made with a predetermined interval using the plasma discharge condition shown in Table 3. The apparatus is operated for other purposes with the condition shown in Table 2.

FIG. 8 is a graph illustrating the change of the etching rate of 0.30 μm^(Φ) hole in relation to the cumulative RF discharge time of the two focus rings 24 (i.e., the cumulative time of RF discharge made using the two focus rings 24). FIG. 8 shows that the change of the etching rate is small even when the cumulative RF discharge time reaches 1200 hours, or when the cumulative RF discharge time of each focus ring 24 reaches 600 hours.

On the other hand, as shown in FIG. 6, the etching rate in the conventional apparatus changes significantly when the cumulative RF discharge time of the focus ring exceeds 300 hours. Accordingly, it can be understood that by employing the ceramic ring 30, the life, or the maximum usable period of the focus ring 24, can be extended at least by two times.

During the experiment, the lower electrode 18 is not damaged. In this experiment, the ceramic ring 30 is prepared separately from the lower electrode 18 and fitted to the side surface 18 b of the lower electrode 18 when starting the experiment. Because the ceramic ring 30 has a smaller outer diameter, and a smaller weight, than those of the focus ring 24, it can be easily fitted to the lower electrode 18. Therefore, there is no risk of damaging the fluorocarbon resin film 20 a on the side surface 18 b of the lower electrode 18 when fitting the ceramic ring 30. Moreover, it is not necessary to detach the ceramic ring for mechanical cleaning.

Finally, FIG. 9 is a graph illustrating the amount of erosion, or the amount of decrease of the thickness (the dimension in the direction perpendicular to the side surface 18 b), of the ceramic ring 30 in relation to the cumulative RF discharge time of the ceramic ring 30, or the cumulative time of RF discharge made using the two focus rings 24 and the ceramic ring 30. Specifically, FIG. 9 shows the maximum amount of erosion measured at a position near the to end of the ceramic ring 30. FIG. 9 indicates that the amount of erosion is about 1 mm when the cumulative RF discharge time is 1200 hours. That is, for example, the ceramic ring 30 with a thickness of 2 mm has a sufficient shielding ability to prevent the plasma from touching the side surface 18 b of the lower electrode 18, at least to the cumulative RF discharge time of 1200 hours.

FIG. 9 shows that, during the initial period before the cumulative RF discharge time of less than about 300 hours, the erosion rate of the ceramic material measured by the amount of erosion of the ceramic ring 30 in the direction perpendicular to the side surface 18 b of the lower electrode 18 is about 25 nm/min. On the other hand, FIG. 3 shows that, during the same time period, the erosion rate of quartz measure by the amount of erosion of the focus ring in the vertical direction, or in the direction perpendicular to the surface of the wafer W, is about 56 nm/min. That is, the erosion rate of the ceramic material measured by the amount of erosion of the ceramic ring 30 in the direction perpendicular to the side surface 18 b of the lower electrode 18 is less than a half of the erosion rate of quartz measured by the amount of erosion of the focus ring 24 in the direction perpendicular to the surface of the wafer W.

FIG. 9 further indicates that, when the cumulative RF discharge time increases, the amount of erosion of the ceramic ring 30 tends to saturate. That is, the erosion rate of the ceramic ring decreases as the cumulative RF discharge time increases. The lower erosion rate of the ceramic ring 30, compared with that of the focus ring 24, enables to use the ceramic ring 30 for a long period even after the focus ring 24 is severely eroded.

It should be noted that the erosion rates and the ratios thereof thus calculated from the data shown in FIGS. 3 and 9 are determined not only by the difference of the properties of the materials but also by the positions of the ceramic ring 30 and the focus ring 24 in the plasma processing apparatus 10. In fact, it is found that the erosion rate of alumina measured by an etching rate of aluminum oxide film on the surface of a wafer W placed on the wafer-supporting surface 18 a of the plasma processing apparatus 10 is about 30 times lower than the erosion rate of quartz measured by an etching ration of silicon dioxide film on the surface of a wafer W placed on the wafer-supporting surface 18 a. It is clear however that the actual erosion rate in the ceramic ring 30 fitted in the processing apparatus 10 determines the usable life of the ceramic ring 30.

This invention is not limited to the specific embodiments described above. Various improvements or modifications may be made within the spirit of this invention.

For example, in the exemplary embodiment described above, a lower electrode 18 having a film of fluorocarbon resin 20 a, which has a superior plasma resistance among resin materials, on the side surface 18 b, is used in order to be compared to the conventional plasma processing apparatus. However, a film of various other resin materials may be used to cover the side surface 18 b of the lower electrode, because the ceramic ring 30 prevents the plasma from touching the side surface 18 b of the lower electrode 18 even after the focus ring 24 is severely eroded. Furthermore, essentially the same usable life of the lower electrode 18 is realized even if the resin film 20 a on the side surface 18 b of the lower electrode 18 is omitted.

Further, in the exemplary embodiments described above, the lower electrode 18 having an electrostatic chuck 20 formed of fluorocarbon resin is used. However, this invention may also be applied to an apparatus having an electrostatic chuck formed of ceramics. In that case, similarly to a case where an electrostatic chuck formed of fluorocarbon resin is used, a ceramic coating film on the side surface 18 b of the lower electrode 18 is not always required.

According to various exemplary embodiments, when the ceramic coating film on the side surface 18 b of the lower electrode 18 is made, however, the ceramic ring 30 prevents the plasma from touching the ceramic coating film on the side surface 18 b of the lower electrode 18 even after the focus ring 24 is severely eroded. Further, different from the ceramic coating formed on the side surface 18 b of the lower electrode, the ceramic ring 30, which is prepared separately from the lower electrode 18, may be replaced with a new one when it is severely eroded. Accordingly, the ceramic ring 30 significantly extends the life of the ceramic coating.

In the exemplary embodiment described above, the ceramic ring 30 has a constant thickness (the dimension perpendicular to the side surface 18 b of the lower electrode 18) throughout the entire height along the side surface 18 b of the lower electrode. Therefore, the entire portion of the ceramic ring 30 is positioned inside the outer perimeter of the wafer W supported on the supporting surface 18 a. However, the ceramic ring 30 may have various shapes other than that shown in the exemplary embodiment. For example, as in the case of the alumina ring shown in Patent Document 3, the ceramic ring may have an extension beneath the focus ring 24. The focus ring 24 prevents the charged particles accelerated toward the direction perpendicular to the surface of the substrate from irradiating such an extended portion, unless the entire thickness of the focus ring 24 is eroded. Therefore, the extended portion of the ceramic ring 30 does not influence the plasma.

Accordingly, a portion of the ceramic ring 30 may position outside the outer perimeter of the wafer W as long as the focus ring 24 or another component prevents the accelerated charged particles from irradiating that portion of the ceramic ring 30 even after the focus ring 24 or the other component is severely eroded by the plasma. In other words, as long as an outer perimeter of the portion of the ceramic ring 30, which is exposed to the plasma when the focus ring 24 or the other component is severely eroded, is positioned approximately aligned with, or inside, the outer perimeter of the wafer W, another portion of the ceramic ring 30 may position outside the outer perimeter of the wafer W. 

1. A plasma processing apparatus for processing a substrate using a plasma, comprising: a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a dimension approximately the same as, or smaller than, a dimension of the substrate; a side surface protecting ring that covers the side surface of the lower electrode, the side surface protecting ring being formed of a ceramic material, an outer perimeter of the side surface protecting ring being positioned approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface; and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring, the focus ring being formed of a first material different from the ceramic material.
 2. The apparatus according to claim 1, wherein the ceramic material has a different secondary electron emission coefficient than that of the first material.
 3. The apparatus according to claim 1, wherein the outer perimeter of the side surface protecting ring is positioned inside the outer perimeter of the substrate.
 4. The apparatus according to claim 1, wherein the side surface protecting ring is prepared separately from the lower electrode and fitted to the side surface of the lower electrode.
 5. The method according to claim 1, wherein the ceramic material having an erosion rate by the plasma lower than an erosion rate of the first material.
 6. The apparatus according to claim 5, wherein the erosion rate of the ceramic material measured by an amount of erosion of the side surface protecting ring in a direction perpendicular to the side surface of the lower electrode is less than half the erosion rate of the first material measured by an amount of erosion of the focus ring in a direction perpendicular to a surface of the substrate supported on the supporting surface.
 7. The method according to claim 1, wherein: the ceramic material is selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution; and the first material is selected from a group consisting of quartz, silicon, and engineering plastics.
 8. The apparatus according to claim 1, wherein the ceramic material is alumina, and the first material is quartz.
 9. A plasma processing apparatus for processing a substrate using a plasma, comprising: a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a dimension smaller than a dimension of the substrate; a side surface protecting ring that covers the side surface of the lower electrode, the side surface protecting ring being formed of a ceramic material; and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring, the focus ring being formed of quartz.
 10. The apparatus according to claim 9, wherein the ceramic material is selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution.
 11. The apparatus according to claim 9, wherein the ceramic material is alumina.
 12. The apparatus according to claim 9, wherein the side surface protecting ring is prepared separately from the lower electrode and fitted to the side surface of the lower electrode.
 13. A method of processing a substrate using a plasma, comprising: providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a dimension approximately the same as, or smaller than, a dimension of the substrate; covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material; surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material different from the ceramic material; supporting the substrate on the supporting surface; and processing a surface of the substrate by generating a plasma in the processing chamber, the processing including: preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode; and preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.
 14. The method according to claim 13, wherein: the focus ring prevents the plasma from touching the side surface protecting ring before the focus ring is eroded by the plasma; and the side surface protecting ring prevents the plasma from touching the side surface of the lower electrode even after the focus ring is eroded by the plasma to an extent that the focus ring cannot prevent the plasma from touching the side surface of the lower electrode.
 15. The method according to claim 13, wherein the ceramic material has a different secondary electron emission coefficient than that of the first material.
 16. The method according to claim 13, wherein said covering includes positioning an outer perimeter of the side surface protecting ring approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface.
 17. The method according to claim 13, wherein said covering includes positioning an outer perimeter of the side surface protecting ring inside an outer perimeter of the substrate supported on the supporting surface.
 18. The method according to claim 13, wherein said covering includes fitting the side surface protecting ring, which is prepared separately from the lower electrode, to the side surface of the lower electrode.
 19. The method according to claim 13, wherein: the ceramic material is selected from the group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution; and the first material is selected from a group consisting of quartz, silicon, and engineering plastics.
 20. The method according to claim 13, wherein the ceramic material is alumina and the first material is quartz.
 21. A method of processing a substrate using a plasma, comprising: providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a dimension smaller than a dimension of the substrate; covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material; surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of quartz; supporting the substrate on the supporting surface; and processing a surface of the substrate by generating a plasma in the processing chamber, the processing including: preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode; and preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.
 22. The method according to claim 21, wherein the ceramic material is selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution.
 23. The method according to claim 21, wherein the ceramic material is alumina.
 24. The method according to claim 21, wherein said covering includes positioning an outer perimeter of the side surface protecting ring approximately aligned with, or inside, an outer perimeter of the substrate supported on the supporting surface.
 25. The method according to claim 21, wherein said covering includes fitting the side surface protecting ring, which is prepared separately from the lower electrode, to the side surface of the lower electrode. 